1. Field of the Invention
The present invention pertains to an apparatus for capturing digital radiographic images. More particularly, the present invention relates to a sensor panel for capture and read-out of electrical charges representing a latent radiographic image using an array of sensors having an extended charge collecting element to obtain an electrical signal representing a radiogram.
2. Description of the Related Art
Radiograms have been produced by using a radiation-sensitive layer to capture a latent radiographic image, as contrasted with traditional radiography which employs a silver halide photosensitive film. Depending on the intensity of the incident radiation, charges are generated within a pixel (picture element) defining the smallest resolvable image area, either electrically or optically by the X-ray radiation, and are quantized using a regularly arranged array of discrete sensors, each of which includes a switching device for read-out. U.S. Pat. No. 5,319,206, issued to Lee et al. on Jun. 7, 1994 and assigned to E. I. du Pont de Nemours and Company, describes a system employing a photoconductive layer to create an image-wise modulated a real distribution of electron hole pairs which are subsequently converted to corresponding analog pixel values by an electrosensitive device, such as a thin-film transistor. U.S. Pat. No. 5,262,649, issued to Antonuk et al. on Nov. 16, 1993 and assigned to University of Michigan, describes a system employing a phosphor or scintillation layer to create a distribution of photons which are subsequently converted to a corresponding image-wise modulated distribution of electrical charges by a photosensitive device, such as an amorphous silicon diode. U.S. Pat. No. 5,254,480, issued to Tran on Oct. 19, 1993 and assigned to 3M Company, describes a system which combines a luminescent layer to create a distribution of photons with an adjacent photoconductive layer to create a corresponding image-wise modulated distribution of electrical charges which are subsequently converted to corresponding analog pixel values by an electrosensitive device.
A common characteristic of all these systems is that the electrosensitive or photosensitive devices capture signal charges within discrete pixel areas confined by typically orthogonally intersecting columns and rows of non-pixel spacings. This feature detracts from the image-wise modulated a real distribution of electrical charges available for read-out. Another characteristic of these systems is that the switching device itself may be adversely affected by electrical charges which are not removed by the charge-collecting portion of the sensor and, thus, remain in proximity to the active portion of the switching device. A further characteristic of these systems is that the signal charges captured within each pixel area are partially limited by the area occupied by the switching device. All of these characteristics combine to reduce the signal-to-noise ratio of the captured pixel values, thereby reducing the quality of the imaging process or possibly requiring an increased radiation exposure of a patient being examined.